The present invention relates generally to applying a coating on a workpiece, and more particularly to an electroplating apparatus and to a method for making an electroplating anode assembly.
It is known to coat turbine airfoils, such as turbine airfoils of an aircraft engine, with platinum aluminide diffusion coatings for protection against high temperature oxidation and corrosion. To develop the platinum aluminide coating, the parts are first platinum electroplated. It is known to use the electrolyte Pt(NH3)4HPO4 for platinum electroplating turbine airfoils.
In a known electroplating method, a cathode rack supports several turbine airfoils and an anode rack supports several electroplating anode assemblies. The turbine airfoils and the electroplating anode assemblies are in contact with the Pt(NH3)4HPO4 electrolyte, and a rectifier is employed to apply a voltage between the cathode and anode racks for platinum electroplating of the turbine airfoils. Each electroplating anode assembly has TIG (Tungsten-Inert-Gas) butt welded together first, second and third structural anode titanium (or titanium alloy) sheet-metal plate members. A conforming platinum-clad niobium anode mesh (i.e., an anode mesh having a shape which substantially conforms to the shape of a surface portion of a turbine airfoil) is supported by two of the first, second, and third structural anode plate members. The anode mesh is electrochemically active during electroplating while the sheet-metal plate members build up an anodic film and passivate during the electroplating process. Difficulties in precisely positioning the plate members for welding often result in plate positioning errors which lead to undesirable coating thickness variations, blistered platinum deposits, no platinum deposits due to short circuits, and damage to anode assemblies and turbine airfoils when the cathode and anode racks are brought into position for electroplating.
Still, scientists and engineers continue to seek improved electroplating apparatus and improved methods for making an electroplating anode assembly.